Following Distances and Road Crashes

Following Distances

The Dangers of Tailgating / Insufficient Following Distances

Most rear-end collisions are caused when drivers do not obey sufficient following distances. This is also known as Tailgating- often regarded as a form of aggressive driving behaviour. In South Africa, with the high prevalence of road rage, tailgating might contribute towards retaliation by other drivers and initiate instances of road rage.

Adequate following distances enable drivers to adjust in emergency situations and bring their vehicles to a stop safely – time that could mean the difference between life and death.

Total stopping distance involves the following:

Human perception time: The time required for a driver to recognise a potential hazard. This time is assumed to be approximately 0.75 seconds in normal situations

Human reaction time: Once the hazard has been perceived, the driver must respond by applying the brakes. The average reaction time is about 0.75 seconds

Vehicle reaction time: This is the time it takes for the vehicle to react once the brakes have been applied by the driver. Vehicle reaction time is very quick, usually assumed to be about 0.05 seconds.

Vehicle braking capability. This refers to the vehicle’s ability to come to a complete stop once the brakes have been applied

International studies have indicated that when a driver follows another vehicle at 100 kilometres per hour and the vehicle in front suddenly applies the brakes, the driver following will need about one and a half seconds to react. If there is not enough distance between the vehicles – the driver following would not be able to stop.

A driver should stay alert at all times as abrupt stopping could be caused by a variety of unforeseen events such as:

debris on the road

pedestrians or stray animals

other drivers falling asleep, drunk drivers or drivers swerving across the road to evade hazards

drivers being distracted, i.e. answering cellular telephone calls etc

The 2-3 Second Rule

Most International road safety campaigns refer to the “2" or "3" Second Rule” as a guideline for safe following distances. A point on the road is noted, 2-3 seconds are counted, and if that point is still visible then there's probably enough following distance.

We agree with the National Safety Council that a three-second rule -- with increases of one second per factor of driving difficulty -- is more appropriate

The 2-3 Second Rule is applied as follows:

Watch the vehicle in front of you pass a landmark - such as a sign, tree, or power pole - at the side of the road.

As it passes the landmark, start counting "one thousand and one, one thousand and two, one thousand and three".

If you pass the landmark before you finish saying all these words, you are following too closely. Slow down, pick another landmark and repeat the words, to make sure you have increased your following distance.
This rule will ensure that you keep the correct following distance, no matter what speed you are travelling at.

Adjusting Following Distance

The 2-3 Second Rule is only the advised measure when driving conditions are ideal. This should be seen as a bare minimum and should be adjusted to at least 5-6 Seconds in the following situations:

In adverse weather conditions

Driving on slippery roads

Driving at night

When following vehicles with different characteristics, i.e. motorcycles & trucks